net: dsa: mv88e6xxx: power serdes on/off for 10G interfaces on 6390X

Upon setting the cmode on 6390 and 6390X, the associated serdes
interfaces must be powered off/on.

Both 6390X and 6390 share code to do so, but it currently uses the 6390
specific helper mv88e6390_serdes_power() to disable and enable the
serdes interface.

This call will fail silently on 6390X when trying so set a 10G interface
such as XAUI or RXAUI, since mv88e6390_serdes_power() internally grabs
the lane number based on modes supported by the 6390, and returns 0 when
getting -ENODEV as a lane number.

Using mv88e6390x_serdes_power() should be safe here, since we explicitly
rule-out all ports but the 9 and 10, and because modes supported by 6390
ports 9 and 10 are a subset of those supported on 6390X.

This was tested on 6390X using RXAUI mode.

Fixes: 364e9d77

 ("net: dsa: mv88e6xxx: Power on/off SERDES on cmode change")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>